Preparation And Performance Characterisation Of Smart Nitrifying Bacteria Gel Spheres

With the continuous urbanisation and development of industrial level in China,the problem of water pollution is becoming more and more prominent.As one of the main excessive pollutants in water quality problems,the effective control of ammonia nitrogen content is of great significance to the prevention and control of water pollution.Biological denitrification technology is theoretically mature and widely used in the field of wastewater treatment.Nitrifying bacteria are the main functional bacteria in the biological denitrification process,which have long generation cycles and are easily influenced by external environmental factors,and easily lost with the water body.In addition,the complex and poorly controlled wastewater quality and irregular changes in temperature and pH inhibit the activity of nitrifying bacteria to different degrees,which also lead to different degrees of failure of the biological denitrification process in industrial wastewater.In this experiment,CA gel spheres were prepared using SA as the substrate,modified with NaCl solution,and the optimal ratios of temperature and pH response layers were investigated by response surface method.The following conclusions were obtained.Through orthogonal experiments,the sphericity,swelling,mechanical properties,oscillation breakage rate and mass transfer performance were used as comprehensive evaluation indexes,and it was concluded that the CA gel spheres made with SA concentration of 3%,CaCl2 concentration of 2%,gelling time of 40h and drop height of 14cm possessed the optimal performance;through single-factor experiments,it was determined that the CA gel spheres modified by 0.6%NaCl solution had the best mass transfer performance of the CA gel spheres modified with 0.6%NaCl solution was determined by single-factor experiments,and they had good resistance to external pressure;the optimal synthesis conditions for the smart gel spheres were determined by the response surface method when the temperature response solution was 15.0mL and the pH response solution was 10.0mL,and the masses of NIPAAm,MBA1,AA and MBA2 were 5.00,2.52,405.61 and 26.21mg,respectively.The swelling rates of CA gel spheres,NaCl modified gel spheres and smart gel spheres were measured under different temperature and pH conditions,which proved that the smart gel spheres were tolerant to temperature and pH.The results of scanning electron microscopy on the gel spheres showed that compared with the CA gel spheres,the NaCl-modified gel spheres showed a clear delamination from the outside to the inside,and the profile of the smart gel spheres showed a shell-core structure(dense outside and sparse inside),which confirmed the successful development of the best dual-response gel spheres and the formation of smart gel spheres with CA as the core and the temperature/pH-responsive layer as the shell layer;infrared analysis showed that the modified Na+and Ca2+substitution occurring on the structure of CA nitrocellulose microspheres,the appearance of C=O stretching vibrational peaks(characteristic peaks of carboxyl groups),the appearance of isopropyl and-NH2,further demonstrating the temperature and pH sensitivity of the smart gel spheres;the increased O and N in the dual response gel spheres compared to the CA gel spheres may be due to the introduction of NIPAAm and AA.After 15 days of the activated sludge incubation,the reactor was considered to be successfully started when the ammonia removal rate in the nitrifying bacteria enrichment system was>90%,the ammonia nitrogen in the effluent was<lmg·L-1,and there was almost no accumulation of NO2--N in the effluent;the sludge colour changed from dark brown to yellowish brown and had good settling performance;the domesticated sludge flocs were dense,without loose structures and with small floc size;In addition,a variety of unicellular and multicellular animals were observed in the sludge,indicating the good performance of the domesticated sludge;at the same time,the microbial population structure showed a good enrichment of nitrifying bacteria.The activated sludge,domesticated sludge and intelligent nitrifying bacteria microspheres were applied to simulated wastewater treatment.Under the same environment,when the temperature was suitable,the treatment effect of domesticated sludge on ammonia nitrogen was slightly better than that of encapsulated nitrifying bacteria,and much better than that of water plant sludge;with the extension of operation time,the loss of free nitrifying bacteria with the water body,and when the temperature change was in low temperature environment,the advantage of encapsulated nitrifying bacteria was highlighted,and the denitrification effect was better than that of free nitrifying bacteria,reflecting the protective effect of the carrier on microorganisms;intelligent nitrifying bacteria microspheres was swelling and breakage of the microspheres late in the run,indicating a service life of around 40 days.Under low temperature conditions,the nitrogen removal effect of immobilised nitrifying bacteria was significantly higher than that of free bacteria;the nitrogen removal performance of free and immobilised nitrifying bacteria showed a trend of increasing and then decreasing with the increase of pH,and overall,the degradation effect of immobilised microorganisms was higher than that of free microorganisms.Due to the protective and buffering effects of the immobilised carriers,the encapsulated nitrifying bacteria particles showed higher nitrification activity over a wider temperature and pH range than the free nitrifying bacteria.